According to a definition approved by a joint Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO) expert Consultation on Health and Nutritional properties of powder milk with live lactic acid bacteria in 2001, probiotics are “live microorganisms which when administered in adequate amounts confer a health benefit on the host”. Probiotic bacteria have been described among species belonging to the genera Lactobacillus, Bifidobacterium, Streptococcus and Lactococcus, which are commonly used in the dairy industry. Probiotics are thought to intervene at the level of the gut microbiota by impeding the development of pathogenic microorganisms and/or by acting more directly on the immune system.
Opportunistic bacterial infections responsible for healthcare associated infections (HAIs) contribute significantly to patient mortality and morbidity, as well as healthcare costs both in developed and developing countries (WHO, 2008). The gastrointestinal tract (GIT) is a reservoir for opportunistic pathogens, which benefit from the disruption of the intestinal microbiota balance, or dysbiosis, to invade and infect susceptible patients. Antibiotic treatments have deleterious effects on the diversity of the intestinal microbiota and they promote expansion of bacterial human opportunistic pathogens including Enterococcus faecalis, Enterococcus faecium or Clostridium difficile. 
Having acquired antibiotic resistance and other pathogenic traits, multi-drug resistant colonizing and/or invasive E. faecalis isolates, which cause serious nosocomial infections, are grouped in seven hospital-adapted complexes designated as High-Risk Enterococcal Clonal Complexes (HiRECCs). Proliferation and persistence of HiRECCs within the GIT are a major risk of developing a vancomycin-resistant enterococcal (VRE) infection, highlighting a need for a better understanding of the biological and biochemical factors involved in colonization of the GIT by E. faecalis. Isolates belonging to HiRECC-2 are among the most common causes of E. faecalis infections in the United States and in several European countries. Some E. faecalis strains acquired pathogenic traits and can cause severe infections. Indeed, they can colonize the GIT and/or cross the intestinal epithelial barrier and enter the bloodstream. Futhermore, Enterococcus spp. contribute to community-acquired intra-abdominal infections and count among the ten most frequently isolated micro-organisms in healthcare-associated infections (HCAI). Hence, reducing the proliferation and persistence of E. faecalis, especially of HiRECCs in the GIT reduces the risk of developing not only a GIT infection, but also an intra-abdominal infection.
It is clear from the above that there is a need for alternatives or complements to antibiotics for the treatment or for the prevention of E. faecalis infection.
The “gut microbiota” designates the population of microorganisms living in the intestine of any organism belonging to the animal kingdom (human, animal, insect, etc.). While each individual has a unique microbiota composition (60 to 80 bacterial species are shared by more than 50% of a sampled population of a total of 400-500 different bacterial species/individual), it always fulfils similar main physiological functions and has a direct impact on the individual's health:                it contributes to the digestion of certain foods that the stomach and small intestine are not able to digest (mainly non-digestible fibers);        it contributes to the production of some vitamins (B and K);        it protects against aggressions from other microorganisms, maintaining the integrity of the intestinal mucosa;        it plays an important role in the development of a proper immune system;        a healthy, diverse and balanced gut microbiota is key to ensuring proper intestinal functioning.        
Taking into account the major role that gut microbiota plays in the normal functioning of the body and the different functions it accomplishes, it is sometimes considered to be an “organ”. However, it is an “acquired” organ, as babies are born sterile; that is, intestine colonization starts at birth and evolves afterwards.
The magnitude of disturbance of the gut microbiota following a perturbation such as a dietary change, an antibiotic treatment and an invasion by an exogenous microbe, and the speed and extent of the recovery to the pre-perturbation state, was defined as “the resilience of the microbiota”. Resilience of the microbiota varies across individuals and between different perturbations within an individual.
From the above, it appears that there is also an important need for treatments for increasing the resilience of the microbiota.
Growing evidence shows that probiotics or fecal microbiota transplantation prevent or treat a number of diseases, including intestinal infections. Such approaches were also associated with higher clearance of intestinal VRE in mice.
Surprisingly the inventors have found that the bacterial species Lactobacillus paracasei is capable of promoting recovery of intestinal microbiota diversity and/or decreasing the load of E. faecalis strains in vivo.
Accordingly, a subject of the present invention is the use of Lactobacillus paracasei, for increasing the resilience of the gut microbiota. In particular, the present invention pertains to the use of Lactobacillus paracasei, for the increase of intestinal microbiota diversity of a subject. In a specific embodiment, the present invention consists in the use of a Lactobacillus paracasei strain for accelerating the decrease of Enterococcus faecalis in the intestinal microbiota of a subject having an intestinal dysbiosis caused by antibiotics.
Further aspects of the present invention provide the use of Lactobacillus paracasei in the prevention, reduction or treatment of intestinal dysbiosis; and/or prevention of a disease caused by a pathogen present in the gastrointestinal tract; and/or increase in the level of short-chain fatty acid in a subject.
The invention also provides compositions comprising Lactobacillus paracasei for use according to the present invention.